How to prevent Safari from squaring the circle at the edges?

.glow-on-hover {
        width: 90%;
        height: 0;
        border: none;
        z-index: 0;
        outline: none;
        background: #111;
        cursor: pointer;
        padding-bottom: 90%;
        border-radius: 50%;
        color: white;
        position: relative;
        height: 50px !important;
    }

    .glow-on-hover img {
        position: absolute;
        top: 50%;
        left: 50%;
        -webkit-transform: translate(-50%, -50%);
        -ms-transform: translate(-50%, -50%);
        transform: translate(-50%, -50%);
        width: 60%;
        height: 60%;
    }

    .glow-on-hover:before {
        content: '';
        background: linear-gradient(45deg, #ff0000, #ff7300, #fffb00, #48ff00, #00ffd5, #002bff, #7a00ff, #ff00c8, #ff0000);
        position: absolute;
        top: -2px;
        left: -2px;
        background-size: 400%;
        z-index: -1;
        filter: blur(5px);
        width: calc(100% + 4px);
        height: calc(100% + 4px);
        animation: glowing 20s linear infinite;
        opacity: 0.7;
        transition: opacity .3s ease-in-out;
        border-radius: 50%;
    }

    .glow-on-hover:active:after {
        top: +2px;
        left: +2px;
        height: calc(100% - 4px);
    }

    .glow-on-hover:hover:before {
        opacity: 1;
        width: calc(100% + 12px);
        height: calc(100% + 12px);
        top: -6px;
        left: -6px;
    }

    .glow-on-hover:after {
        z-index: -1;
        content: '';
        position: absolute;
        width: 100%;
        height: 100%;
        background: #111;
        left: 0;
        top: 0;
        color: white;
        border-radius: 50%;
    }

<div style="height:200px; width: 200px;">
<button class="glow-on-hover">
</div>